4.2L engine, about 78,000 miles. Sometimes runs fine, sometime runs rough, stalls and throws codes usually misfire detected #2 cylinder, but sometimes random misfire detected. Fuel pressure at idle fluctuates rapidly between 58 and 65, smoths out at higher RPM. Replaced plugs, #2 coil, cleaned throttle body and MAF sensor. Continues. May run good for weeks and thousands of miles then acts up again. Been chasing this problem for 18 months. Any ideas?